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20 Cards in this Set

  • Front
  • Back
4 Enzymes in Glycogenolysis
alpha 1,6 glucosidase
Products of removing glucose
by Glycogen Phosphorylase

Glycogen + Glusose 1--phosphate

Adds a phosphate group=uses this energy instead of burning ATP
Coenzyme of Glycogen Phosphorylase?
Vitamin B6=Pyroxydil

Covalently bonded to enzyme
e-donor,hands off e- to rest of molecule
3 Enzymes=3 Steps
Step 1
Glycogen Phosphorylase
breaks unbranced chains by phophorolysis=break bond and turn bonded glucose end to a phosphate group
*maked Glucose-1-pi*
2 forms
a=active has a pi
b=inactive and no pi
3 Enzymes=3 Steps
step 2
called when glycogen phosphorylase gets to branch

extend by 3 glusoses
3 Enzymes=3 Steps
Step 3
then breaks at branch point by hydrolysis
Adds a pi to the liberated Glucose 6-Pi to make Glucose 1,6 bisphosphate
Enzyme then grabs a Pi and makes Glucose 6 pi
*in equil. with Glucose 1-pi, so can go to storage or usage*
Regulation of Glycogen Metabolism

Allosteric Regulation of breakdown in Liver and Muscle
Allosteric in Liver=Glucose

Allosetric in Muscle=Energy state, ATP, AMP, Glucose 6-pi
Glycogen Phosphorylase
Inactive=de pi

If glucose level is high it can bind and shut down enzyme even if PI
Glycogen Phosphorylase
Active=pi, AMP forces in to active form even if de-pi

Inactive=de-pi, ATP forces into inactive form

ATP and AMP compete for active site
Glycogen Synthase
Muscle and Liver
Active=de pi

Glucose can allosterically regulate and force into active form even if it is pi
Hormonal Control of Glycogen Metabolism
Insulin=released from B cells if Glucose high
Glucagon=Islet cells, stimulates breakdown of glycogen
Epinephrine=adrenal medula, stress,
insert insulin mechanism pic.
Extra step
Phosphorylase kinase takes glycogen phosphorylase to active state

Ca2+ can bind to the kinase and super stimulate it
insert dual pathway pic.
Breakdown and Synthesis are on all the time
Glycogen phophatase complex

Rg1=regulatory unit

Glycogen molecule
insert phosphotase complex pic
PP1= slows glycogen breakdown
Active=complex is associated with Glycogen particle,active is when Rg1 is NOT pi
PKA=pi's the RG1 and and PP1 won't bind complex so it isnt closely associated with Glycogen, so LESS ACTIVE
PKA=adds pi to inhibitor and inhibitor binds PP1 and it is totally inactive
insulin stim of glycogen synth pic.
Insulin binds receptor tyrosine kinase, reacts with insulin sensitive protein kinase
adds pi to RG1 insulin specific site which then retains PP1 by glycogen and hence active, hence stops breakdown of glycogen
Hormonal Stimulation of Glycogen Synthesis
Insulin (mostly liver but some effect in muscle) stimulates glycogen synthesis via Protein phosphatase 1 (PP1) which de-phosphorylates the following:

Phosphorylase kinase - now inactive

Glycogen phosphorylase - now inactive

Glycogen synthase - now active

Protein phosphatase 1 complex -
PI-regulatory subunit - binds PP1 subunit
no P on inhibitor subunit - now inactive

PP1 has an effect opposite that of PKA!
Hormonal Stimulation of glycogenolysis
Glucagon (liver) and epinephrine (muscle) stimulate glycogen breakdown via Protein kinase A (PKA) which phosphorylates the following:

Phosphorylase kinase - now active

Glycogen phosphorylase - now active

Glycogen synthase - now inactive

Protein phosphatase 1 complex -
PE+G-regulatory subunit - releases PP1 subunit
P-inhibitor subunit - binds and impairs PP1 subunit
Hormonal Control of Glycogen Metabolism
insert picture lecture 59 p. 16